Low-K Gate Spacer and Methods for Forming the Same

ABSTRACT

Embodiments of the present disclosure relate to a FinFET device having gate spacers with reduced capacitance and methods for forming the FinFET device. Particularly, the FinFET device according to the present disclosure includes gate spacers formed by two or more depositions. The gate spacers are formed by depositing first and second materials at different times of processing to reduce parasitic capacitance between gate structures and contacts introduced after epitaxy growth of source/drain regions.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No. 15/812,966, filed on Nov. 14, 2017, which is hereby incorporated herein by reference.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. However, these advances have increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. When a semiconductor device such as a fin like field-effect transistor (FinFET) is scaled down through various technology nodes, several strategies have been employed to improve device performance, such as using epitaxy channels to enhance carrier mobility.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

FIG. 1 is an example of simplified Fin Field Effect Transistor (FinFET) devices in a three-dimensional view in accordance with some embodiments.

FIGS. 2A-C, 3A-C, 4A-C, 5A-C, 6A-C, 7A-C, 8A-C, 9A-C, 10A-C, 11A-C, 12A-C, 13A-C, 14A-C, 15A-C, 16A-C, 17A-C, 18A-C, 19A-C, 20A-C, 21A-C, 22A-C, 23A-C, 24A-C, 25A-C, 26A-C, 27A-C, and 28A-C are cross-sectional views of respective intermediate structures during intermediate stages in an example process of forming a gate structure with gate spacers in FinFET devices in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

Embodiments of the present disclosure relate to a FinFET device having gate spacers with reduced capacitance and methods for forming the FinFET device. Particularly, the FinFET device according to the present disclosure includes gate spacers formed by two or more depositions. The gate spacers are formed by depositing first and second materials at different times of processing to reduce parasitic capacitance between gate structures and contacts introduced after epitaxy growth of source/drain regions.

FIG. 1 schematically illustrates a device 100 in a three-dimensional view. Other aspects not illustrated in or described with respect to FIG. 1 may become apparent from the following figures and description. The device 100 may be part of an IC, such as a microprocessor, memory cell, such as static random-access memory (SRAM), and/or other integrated circuits. The device 100 may be electrically connected or coupled in a manner to operate as, for example, two transistors or more, such as four transistors.

The device 100 may include an N-type FinFET structure 102 and a P-type FinFET structure 104. The N-type FinFET structure 102 includes fins 110 a and 110 c on a P-doped region 106 a. The N-type FinFET structure 102 includes isolation regions 108, and the fins 110 a and 110 c each protrude above and from between neighboring isolation regions 108. Gate stack 150 a is along sidewalls and over top surfaces of the fins 110 a and 110 c. The gate stack 150 a includes gate dielectric 158 a and gate electrode 154 a over the gate dielectric 158 a. Source/drain regions 156 a-b and 156 c-f are disposed in respective regions of the fins 110 a and 110 c. Source/drain regions 156 a and 156 b are disposed in opposing regions of the fin 110 a with respect to the gate dielectric 158 a and gate electrode 154 a. Source/drain regions 156 e and 156 f are disposed in opposing regions of the fin 110 c with respect to the gate dielectric 158 a and gate electrode 154 a.

In some examples, two transistors may be implemented in the N-type FinFET structure 102 by: (1) source/drain regions 156 a and 156 b and the gate stack 150 a; and (2) source/drain regions 156 e and 156 f and the gate stack 150 a. Some source/drain regions may be shared between various transistors, for example. In some examples, various ones of the source/drain regions may be connected or coupled together such that the N-type FinFET structure 102 is implemented as one functional transistor. For example, if neighboring (e.g., as opposed to opposing) source/drain regions 156 a, 156 e and 156 b, 156 f are electrically connected, respectively, such as through coalescing the regions by epitaxial growth (e.g., source/drain regions 156 a and 156 e being coalesced, and source/drain regions 156 b and 156 f being coalesced), one functional transistor may be implemented. Other configurations in other examples may implement other numbers of functional transistors.

The P-type FinFET structure 104 includes fins 110 b and 110 d on a N-doped region 106 b. The P-type FinFET structure 104 includes isolation regions 108, and the fins 110 b and 110 d each protrude above and from between neighboring isolation regions 108. Gate stack 150 b is along sidewalls and over top surfaces of the fins 110 b and 110 d. The gate stack 150 b includes gate dielectric 158 b and gate electrode 154 b over the gate dielectric 158 b. Source/drain regions 156 c-d and 156 g-h are disposed in respective regions of the fins 110 b and 110 d. Source/drain regions 156 c and 156 d are disposed in opposing regions of the fin 110 b with respect to the gate dielectric 158 b and gate electrode 154 b. Source/drain regions 156 g and 156 h are disposed in opposing regions of the fin 110 d with respect to the gate dielectric 158 b and gate electrode 154 b.

In some examples, two transistors may be implemented in the P-type FinFET structure 104 by: (1) source/drain regions 156 c and 156 d and the gate stack 150 b; and (2) source/drain regions 156 g and 156 h and the gate stack 150 b. Some source/drain regions may be shared between various transistors, for example. In some examples, various ones of the source/drain regions may be connected or coupled together such that the P-type FinFET structure 104 is implemented as one functional transistor. For example, if neighboring (e.g., as opposed to opposing) source/drain regions 156 c, 156 g and 156 d, 156 h are electrically connected, respectively, such as through coalescing the regions by epitaxial growth (e.g., source/drain regions 156 c and 156 g being coalesced, and source/drain regions 156 d and 156 h being coalesced), one functional transistor may be implemented. Other configurations in other examples may implement other numbers of functional transistors.

FIG. 1 further illustrates reference cross-sections that are used in later figures. Cross-section B-B is in a vertical plane along channels in the fins 110 a, 110 b between opposing source/drain regions 156 a-d. Cross-section A-A is in a vertical plane perpendicular to cross-section B-B and is across the source/drain region 156 a in the fin 110 a and across the source/drain region 156 e in the fin 110 c. Cross-section C-C is in a vertical plane perpendicular to cross-section B-B and is across the source/drain region 156 d in the fin 110 b and across the source/drain region 156 h in the fin 110 d. Subsequent figures refer to these reference cross-sections for clarity.

FIGS. 2A-C through 28A-C are cross-sectional views of respective intermediate structures during intermediate stages in an example process of forming a gate structure with gate spacers in, e.g., one or more FinFETs, in accordance with some embodiments. In FIGS. 2A-C through 28A-C, figures ending with an “A” designation illustrate cross-sectional views along a cross-section similar to cross-section A-A in FIG. 1; figures ending with a “B” designation illustrate cross-sectional views along a cross-section similar to cross-section B-B in FIG. 1; and figures ending with a “C” designation illustrate cross-sectional views along a cross-section similar to cross-section C-C in FIG. 1. In some figures, some reference numbers of components or features illustrated therein may be omitted to avoid obscuring other components or features; this is for ease of depicting the figures.

FIGS. 2A, 2B, and 2C illustrate a semiconductor substrate 106 having a fin mask 112 formed thereon for forming fins. The semiconductor substrate 106 may be or include a bulk semiconductor substrate, a semiconductor-on-insulator (SOI) substrate, or the like, which may be doped (e.g., with a p-type or an n-type dopant) or undoped. Generally, an SOI substrate comprises a layer of a semiconductor material formed on an insulator layer. The insulator layer may be, for example, a buried oxide (BOX) layer, a silicon oxide layer, or the like. The insulator layer is provided on a substrate, typically a silicon or glass substrate. Other substrates, such as a multi-layered or gradient substrate may also be used. In some embodiments, the semiconductor material of the semiconductor substrate may include silicon (Si); germanium (Ge); a compound semiconductor including silicon carbide, gallium arsenic, gallium phosphide, indium phosphide, indium arsenide, or indium antimonide; an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, or GaInAsP; or a combination thereof.

The semiconductor substrate 106 includes the P-doped region 106 a and N-doped region 106 b for forming N-type FinFET and P-type FinFET respectively. One or both of the P-doped region 106 a and N-doped region 106 b may be a doped well formed by implantation into the semiconductor substrate 106. For example, the semiconductor substrate 106 can be a P-type doped substrate, a part of which forms the P-doped region 106 a, and the N-doped region 106 b may be an N-doped well formed by implanting N-type dopants into the P-type doped substrate.

The fin mask 112 may be a hard mask used to form the fins 110 a-110 d. For example, one or more mask layers are deposited over the semiconductor substrate 106 in the P-doped region 106 a and the N-doped region 106 b and then patterned into the fin mask 112. In some examples, the one or more mask layers may include or be silicon nitride, silicon oxynitride, silicon carbide, silicon carbon nitride, the like, or a combination thereof, and may be deposited by chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), or another deposition technique. The one or more mask layers may be patterned using photolithography. For example, a photo resist can be formed on the one or more mask layers, such as by using spin-on coating, and patterned by exposing the photo resist to light using an appropriate photomask. Exposed or unexposed portions of the photo resist may then be removed depending on whether a positive or negative resist is used. The pattern of the photoresist may then be transferred to the one or more mask layers, such as by using a suitable etch process, which forms the fin mask. The etch process may include a reactive ion etch (RIE), neutral beam etch (NBE), the like, or a combination thereof. The etching may be anisotropic. Subsequently, the photo resist is removed in an ashing process or wet strip process.

FIGS. 3A, 3B, and 3C illustrate that the semiconductor substrate 106 in the P-doped region 106 a and the N-doped region 106 b is etched to form fins 110 a, 110 c, 110 b′, 110 d′ such that the fins 110 a, 110 c, 110 b′, 110 d′ protrude from the P-doped region 106 a and the N-doped region 106 b. The etch process may include a RIE, NBE, the like, or a combination thereof. The etching may be anisotropic.

As shown in FIGS. 4A, 4B, and 4C, after formation of the fins 110 a, 110 b′, 110 c, 110 d′, an insulating material 107 may be deposited in the trenches between the fins 110 a, 110 b′, 110 c, 110 d′. The insulating material 107 may be an oxide (such as silicon oxide), a nitride, the like, or a combination thereof, and the insulating material may be formed by a high density plasma CVD (HDP-CVD), a flowable CVD (FCVD) (e.g., a CVD-based material deposition in a remote plasma system and post curing to make it convert to another material, such as an oxide), the like, or a combination thereof. Other insulating materials formed by any acceptable process may be used. In the illustrated embodiment, the insulating material 107 includes silicon oxide that is formed by a FCVD process. A planarization process, such as a chemical mechanical polish (CMP), may remove any excess insulating material and any remaining fin mask to form top surfaces of the insulating material and top surfaces of the fins 110 a, 110 b′, 110 c, 110 d′ to be coplanar.

As shown in FIGS. 5A, 5B, and 5C, the fins 110 b′, 110 d′ may be etched back after planarization of the insulating material 107. For example, a mask 116 may be used to cover the P-doped region 106 a so that the fins 110 b′, 110 d′ in the N-doped region 106 b may be etched forming recesses 118 in the insulating material 107.

In FIGS. 6A, 6B, and 6C, replacement fins 110 b, 110 d are formed in the recesses 118 in the N-doped region 106 b by epitaxial growth. In some embodiments, the fins 110 b, 110 d may comprise silicon, silicon germanium (Si_(x)Ge_(1-x), where x can be between approximately 0 and 100), silicon carbide, pure or substantially pure germanium, a III-V compound semiconductor, a II-VI compound semiconductor, or the like. For example, materials for forming a III-V compound semiconductor include InAs, AlAs, GaAs, InP, GaN, InGaAs, InAlAs, GaSb, AlSb, AlP, GaP, and the like. In one embodiment, the replacement fins 110 b, 110 d include silicon germanium to provide improved mobility for P-type FinFET.

In FIGS. 7A, 7B, and 7C, the insulating material 107 is recessed to form the isolation regions 108. The insulating material 107 is recessed such that the fins 110 a, 110 b, 110 c, 110 d protrude from between neighboring isolation regions 108, which may, at least in part, thereby delineate the fins 110 a, 110 b, 110 c, 110 d as active areas in the P-doped region 106 a and N-doped region 106 b. The insulating material 107 may be recessed using an acceptable etching process, such as one that is selective to the material of the insulating material. For example, a chemical oxide removal using a CERTAS® etch or an Applied Materials SICONI® tool or dilute hydrofluoric (dHF) acid may be used. Further, top surfaces of the isolation regions 108 may have a flat surface as illustrated, a convex surface, a concave surface (such as dishing), or a combination thereof, which may result from an etch process.

As shown in FIGS. 8A, 8B, and 8C after formation of the isolation regions 108, dummy gate stacks 120 a, 120 b are then formed on the fins 110 a, 110 b, 110 c, 110 d. Each dummy gate stack 120 a, 120 b includes an interfacial dielectric 122, a dummy gate 124, an etch stop layer 125, and a hard mask 126. The interfacial dielectric 122, dummy gate 124, etch stop layer 125, and hard mask 126 may be formed by sequentially depositing respective layers and patterning those layers. For example, a layer for the interfacial dielectric 122 may include or be silicon oxide, silicon nitride, the like, or multilayers thereof, and may be thermally grown or deposited, such as by plasma-enhanced CVD (PECVD), ALD, or another deposition technique. A layer for the dummy gate 124 may include or be silicon (e.g., polysilicon) or another material deposited by CVD, PVD, or another deposition technique. A layer for the hard mask 126 may include or be silicon nitride, silicon oxynitride, silicon carbon nitride, the like, or a combination thereof, deposited by CVD, PVD, ALD, or another deposition technique. The layers for the hard mask 126, etch stop layer 125, dummy gate 124, and interfacial dielectric 122 may then be patterned, for example, using photolithography and one or more etch processes forming the dummy gate stacks 120 a, 120 b.

In FIGS. 9A, 9B, and 9C, a first spacer layer 128 is formed conformally over the substrate 106. The first spacer layer 128 covers the top surfaces and sidewalls of dummy gate stacks 120 a, 120 b, the top surface of isolation regions 108, and the sidewalls and the top surfaces of the fins 110 a, 110 b, 110 c, 110 d. In some embodiments, the first spacer layer 128 is made of silicon nitride (SiN), silicon oxycarbide (SiOC), silicon oxycarbonnitride (SiOCN), or other applicable dielectric materials. In some embodiments, the first spacer layer 128 includes one or more low-k dielectric materials having a dielectric constant (k) less than 3.9. In one example, the first spacer layer 128 may have a dielectric constant (k) in a range from about 3.9 to about 3.0. The first spacer layer 128 may be formed by plasma enhanced CVD, low pressure CVD, ALD, or other applicable processes.

In some embodiments, the thickness of the first spacer layer 128 is in a range from about 10 angstroms to about 30 angstroms. In some embodiments, the thickness of the first spacer layer 128 is in a range from about 40% to about 60% of a designed thickness of gate spacers.

After the first spacer layer 128 is formed, a sacrificial layer 130 is formed over the first spacer layer 128 as shown in FIGS. 10A, 10B, and 10C. The sacrificial layer 130 is configured to protect the first spacer layer 128 from being damaged during subsequent processes, such as during an epitaxial process to form epitaxial source/drain regions. The sacrificial layer 130 may be a dielectric material that can stand process conditions of an epitaxial deposition process and can be selectively etched away from the first spacer layer 128. For example, the sacrificial layer 130 may include one of silicon nitride, silicon carbide nitride, silicon oxide, silicon oxynitride, or the like. In one embodiment, the sacrificial layer 130 includes silicon nitride. The sacrificial layer 130 may be formed by plasma enhanced CVD, low pressure CVD, ALD, or other applicable processes. The sacrificial layer 130 may have a thickness in a range from about 40 angstroms to about 60 angstroms.

In FIGS. 11A, 11B, and 11C, a hard mask 132 is formed over the P-doped region 106 a to cover the N-type FinFET structure 102 while exposing the P-type FinFET structure 104 in the N-doped region 106 b. The hard mask 132 may be formed through a photolithography process. In one embodiment, the hard mask 132 may be silicon nitride or the like.

In FIGS. 12A, 12B, and 12C, an etch process is performed to expose the fins 110 b, 110 d in the P-type FinFET structure 104 to form source/drain regions therefrom. The etch process is an anisotropic etch process where the sacrificial layer 130 and the first spacer layer 128 are etched along the z-direction while remaining substantially unchanged along the x-direction and the y-direction (as shown in the coordinate system in FIG. 1). The anisotropic etch process may be performed by a RIE, NBE, or other suitable etch process.

As shown in FIG. 12B, the first spacer layer 128 and the sacrificial layer 130 remain on the sidewalls of the dummy gate stack 120 b from up to a middle section of the hard mask 126. In one embodiment, the fins 110 b, 110 d are recessed by a recess amount 110 r. The recess amount 110 r may be in a range from about 0 nm to about 10 nm. The remaining fins 110 b, 110 d above the isolation region 108 are used to be a core for the subsequent epitaxial process.

The sacrificial layer 130 protects the first spacer layer 128 from losing thickness during the etch process to expose the fins 110 b, 110 d. With the first spacer layer 128 remaining over sidewalls of the dummy gate 124, the dummy gate 124 may not suffer any side wall loss or damage during the etch process. With the protection to the first spacer layer 128 at the sidewalls of the dummy gate stack 120 b, the etch process may be performed to completely remove the first spacer layer 128 from a bottom portion of sidewalls 110 s of the fins 110 b, 110 d, thus, preventing poor epitaxial growth caused by the remaining first spacer layer 128 during subsequent epitaxial process and preventing any corner damage caused by the remaining first spacer layer 128 on the sidewalls 110 s of the fins 110 b, 110 d. The sacrificial layer 130 is over the hard mask 126 before the etch process and therefore is not exposed to the etch process during at least a portion of the duration of the etch process, thus, allowing the dummy gate 124 to remain being covered the hard mask 126. With the dummy gate 124 being covered with no undesired exposure, any undesirable epitaxial growth from the dummy gate 124, also known as mushroom defects, may be prevented from occurring during the subsequent epitaxial process. Additionally, the sacrificial layer 130 may also prevent some loss of the isolation regions 108 during the etch process.

In FIGS. 13A, 13B, and 13C, an epitaxial process is performed to grow epitaxial structures 134 b, 134 d from the fins 110 b, 110 d. The epitaxial structures 134 b, 134 d are formed to function as source/drain regions for P-type FinFET devices. The epitaxial structures 134 b, 134 d may include a single-element semiconductor material such as germanium (Ge) or silicon (Si); or compound semiconductor materials, such as gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs); or semiconductor alloy, such as silicon germanium (SiGe), gallium arsenide phosphide (GaAsP). In an embodiment, the epitaxial structures 134 b, 134 d include an epitaxially grown silicon germanium (SiGe) to function as source/drain regions for P-type FinFET devices.

The epitaxial structures 134 b, 134 d are formed by a suitable epitaxial process, for example, a selective epitaxial growth (SEG) process, a chemical vapor deposition (CVD) process (e.g., vapor-phase epitaxy (VPE), a low pressure chemical vapor deposition (LPCVD), and/or ultra-high vacuum CVD (UHV-CVD)), molecular beam epitaxy (MBE), liquid phase epitaxy (LPE), or combinations thereof. The formation process of the epitaxial structures 134 b, 134 d may use gaseous and/or liquid precursors, which may interact with the composition of the fins 110 b, 110 d thereunder.

The epitaxial structures 134 b, 134 d may be doped or undoped in-situ during the epitaxial process. For example, the epitaxially grown SiGe epitaxial structure may be doped with boron. The doping may be achieved by an ion implantation process, plasma immersion ion implantation (PIII) process, gas and/or solid source diffusion process, another suitable process or combinations thereof. The epitaxial structures 134 b, 134 d may further be exposed to an annealing process, such as a rapid thermal annealing (RTA) and/or laser annealing process. The annealing process may be used to activate the dopants. If the epitaxial structures 134 b, 134 d are not doped in-situ, a second implantation process (e.g., a junction implant process) is performed to dope the epitaxial structures 134 b, 134 d.

The epitaxial structures 134 b, 134 d are strained and stressed to enhance carrier mobility of the FinFET device structure and enhance the FinFET device structure performance. The performance of the P-type FinFET structure 104 may be relative to the volume of the epitaxial structures 134 b, 134 d. For example, if the volume of the epitaxial structures 134 b, 134 d is increased, the operation speed of the P-type FinFET structure 104 is also increased. In FIG. 13C, the cross sectional shape of each epitaxial structures 134 b, 134 d is substantially a rhombus shape as a result that silicon germanium is formed more efficiently along its crystal planes. However, the shape of the epitaxial structures 134 b, 134 d is not intended to be limiting.

In FIGS. 14A, 14B, and 14C, the hard mask 132 and the sacrificial layer 130 are removed by an etch process. In one embodiment, the hard mask 132 and the sacrificial layer 130 may be removed by a wet etching process. For example, the hard mask 132 and the sacrificial layer 130 are removed using a wet etchant comprising H₃PO₄. Other suitable etchants, such as HF or the like may also be used.

As shown in FIGS. 15A, 15B, and 15C, after the hard mask 132 and the sacrificial layer 130 are removed, a sacrificial layer 136 may be formed over the substrate 106 over both the P-doped region 106 a and the N-doped region 106 b. The sacrificial layer 136 is configured to protect the first spacer layer 128 during the subsequent fin recess process and epitaxial process in the P-doped region 106 a. The sacrificial layer 136 is similar to the sacrificial layer 130. The sacrificial layer 136 may be a dielectric material that can stand process conditions of an epitaxial deposition process and can be selectively etched away from the first spacer layer 128. For example, the sacrificial layer 136 may include one of silicon nitride, silicon carbide nitride, silicon oxide, silicon oxynitride, or the like. In one embodiment, the sacrificial layer 136 includes silicon nitride. The sacrificial layer 136 may be formed by plasma enhanced CVD, low pressure CVD, ALD, or other applicable processes. The sacrificial layer 136 may have a thickness in a range from about 40 angstroms to about 60 angstroms.

In FIGS. 16A, 16B, and 16C, a hard mask 138 is formed over the N-doped region 106 b to cover the P-type FinFET structure 104 while exposing the N-type FinFET structure 102 in the P-doped region 106 a. The hard mask 138 may be formed through a photolithography process. In one embodiment, the hard mask 138 may be silicon nitride or the like.

In FIGS. 17A, 17B, and 17C, an etch process is performed to recess the fins 110 a, 110 c in the N-type FinFET structure 102 so that epitaxial source/drain regions can be formed. The etch process is an anisotropic etch process where the sacrificial layer 136 and the first spacer layer 128 are etched along the z-direction while remaining substantially unchanged along the x-direction and the y-direction. The anisotropic etch process may be performed by a RIE, NBE, or other suitable etch process.

As shown in FIG. 17B, the first spacer layer 128 and the sacrificial layer 136 remain on the sidewalls of the dummy gate stack 120 a from up to a middle section of the hard mask 126. As shown in FIG. 17A, after the etch process, a spacer portion 128 r of the first spacer layer 128 remains over a top surface 108 s of the isolation regions 108. A height 142 of the spacer portion 128 r may be in a range from about 0 nm to about 10 nm. Recesses 140 are formed between the spacer portions 128 r. The recesses 140 may be used to limit horizontal growth during the initial stage of growing epitaxial source/drain regions.

The sacrificial layer 136 protects the first spacer layer 128 from losing thickness during recessing the fins 110 a, 110 c. With the first spacer layer 128 remaining over sidewalls of the dummy gate 124, the dummy gate 124 in the dummy gate stack 120 a may not suffer any side wall loss or damage during the etch process. With the protection to the first spacer layer 128 at the sidewalls of the dummy gate stack 120 a, the etch process may be performed to control the height 142 of the spacer portion 128 r, thus, achieving suitable height 142 to the dimension of the epitaxial source/drain regions to be grown in the subsequent epitaxial process. With suitable height of the spacer portion 128 r, merging or coalescing of epitaxial source/drain regions between neighboring fins are prevented, thus, improving CD control. The sacrificial layer 136 is over the hard mask 126 before the etch process and therefore is not exposed to the etch process during at least a portion of the duration of the etch process, thus, allowing the dummy gate 124 to remain being covered the hard mask 126. With the dummy gate 124 being covered with no undesired exposure, any undesirable epitaxial growth from the dummy gate 124, also known as mushroom defects, may be prevented from occurring during the subsequent epitaxial process. Additionally, the sacrificial layer 136 may also prevent loss of the isolation regions 108 during the etch process.

In FIGS. 18A, 18B, and 18C, an epitaxial process is performed to grow epitaxial structures 134 a, 134 c from the fins 110 a, 110 c in the recesses 140. The epitaxial structures 134 a, 134 c are formed to function as source/drain regions for N-type FinFET devices. The epitaxial structures 134 a, 134 c may be silicon including N-type dopants, such as phosphorus, carbon, or combinations thereof.

The epitaxial structures 134 a, 134 c are formed by a suitable epitaxial process, for example, a selective epitaxial growth (SEG) process, a chemical vapor deposition (CVD) process (e.g., vapor-phase epitaxy (VPE), a low pressure chemical vapor deposition (LPCVD), and/or ultra-high vacuum CVD (UHV-CVD)), molecular beam epitaxy (MBE), liquid phase epitaxy (LPE), or combinations thereof. The formation process of the epitaxial structures 134 a, 134 c may use gaseous and/or liquid precursors, which may interact with the composition of the fins 110 a, 110 c thereunder.

The epitaxial structures 134 b, 134 d may be doped or undoped in-situ during the epitaxial process. For example, the epitaxially grown Si epitaxial structure may be doped with carbon to form a Si:C epitaxial structure, phosphorous to form a Si:P epitaxial structure, or both carbon and phosphorous to form a SiCP epitaxial structure. The doping may be achieved by an ion implantation process, plasma immersion ion implantation (PIII) process, gas and/or solid source diffusion process, another suitable process, or combinations thereof. The epitaxial structures 134 a, 134 c may further be exposed to an annealing process, such as a rapid thermal annealing (RTA) process and/or laser annealing process. The annealing process may be used to activate the dopants. If the epitaxial structures 134 a, 134 c are not doped in-situ, a second implantation process (e.g., a junction implant process) is performed to dope the epitaxial structures 134 a, 134 c.

The epitaxial structures 134 a, 134 c are strained and stressed to enhance carrier mobility of the FinFET device structure and enhance the FinFET structure performance. As shown in FIG. 18A, epitaxial structures 134 a, 134 c are first grown vertically in the recesses 140, during which time the epitaxial structure 134 a, 134 b do not grow horizontally. After the recesses 140 are fully filled, the epitaxial structures 134 a, 134 b may grow both vertically and horizontally to form facets corresponding to crystalline planes of the substrate 106. In FIG. 18A, the cross sectional shape of each epitaxial structures 134 a, 134 c is substantially a rhombus shape as a result that silicon carbon, silicon phosphorous, or silicon carbon phosphorous is formed more efficiently along its crystal planes. However, the shape of the epitaxial structures 134 a, 134 c is not intended to be limiting.

In FIGS. 19A, 19B, and 19C, the hard mask 138 and the sacrificial layer 136 are removed by an etch process. In one embodiment, the hard mask 138 and the sacrificial layer 136 may be removed by a wet etching process. For example, the hard mask 138 and the sacrificial layer 136 are removed using a wet etchant comprising H₃PO₄. Other suitable etchants, such as HF or the like may also be used.

In FIGS. 20A, 20B, and 20C, a second spacer layer 144 is conformally formed over the substrate 106. The second spacer layer 144 covers the top surface and sidewalls of dummy gate stacks 120 a, 120 b, the top surface of isolation regions 108, and the sidewalls and the top surface of the epitaxial structures 134 a, 134 b, 134 c, 134 d. In some embodiments, the second spacer layer 144 is or includes silicon oxycarbide (SiOC), silicon oxycarbonnitride (SiOCN), or other applicable dielectric materials.

In some embodiments, the second spacer layer 144 includes one or more low-k dielectric materials having a dielectric constant (k) equal to or less than 3.9. In one example, the second spacer layer 144 may include low-k dielectric materials having a dielectric constant (k) in a range from about 3.9 to about 2.5. The second spacer layer 144 may be formed by plasma enhanced CVD, low pressure CVD, ALD, or other applicable processes. In some embodiment, the second spacer layer 144 is a porous dielectric film. The second spacer layer 144 may include pores having a median radius in a range from about 0.4 nm to about 0.43 nm. The second spacer layer 144 may have a porosity in a range between about 2.00% to about 3.50%. For example, the second spacer layer 144 may have a porosity of about 3.27%.

In some embodiments, the thickness of the second spacer layer 144 is in a range from about 20 angstroms to about 40 angstroms. In some embodiments, the thickness of the second spacer layer 144 is in a range from about 40% to about 70% of a designed thickness of gate spacers. In one embodiment, the second spacer layer 144 has a conformity in a range between about 90% to about 100%.

In FIGS. 21A, 21B, and 21C, a contact etch stop layer (CESL) 146 is conformally formed over substrate 106 to cover the second spacer layer 144. In some embodiments, the contact etch stop layer 146 is made of silicon nitride, silicon oxynitride, and/or other applicable materials. The contact etch stop layer 146 may be formed by plasma enhanced CVD, low pressure CVD, ALD, or other applicable processes.

In FIGS. 22A, 22B, and 22C, an inter-layer dielectric (ILD) layer 148 is formed over the contact etch stop layer 146 over substrate 106 in accordance with some embodiments. The inter-layer dielectric layer 148 may include one or multiple layer including dielectric materials, such as silicon oxide, silicon nitride, silicon oxynitride, tetraethoxysilane (TEOS), phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), low-k dielectric material, and/or other applicable dielectric materials. Examples of low-k dielectric materials include, but are not limited to, fluorinated silica glass (FSG), carbon doped silicon oxide, amorphous fluorinated carbon, parylene, bis-benzocyclobutenes (BCB), or polyimide. The inter-layer dielectric layer 148 may be formed by chemical vapor deposition (CVD), physical vapor deposition, (PVD), atomic layer deposition (ALD), spin-on coating, or other applicable processes.

After forming the inter-layer dielectric layer 148, a planarization process is performed to expose the top surface of the dummy gates 124 as shown in FIGS. 23A, 23B, and 23C. In some embodiments, the planarization process may be a chemical mechanical polishing (CMP) process.

After the planarization process, the dummy gates 124 are removed to form trenches 160, as shown in FIGS. 24A, 24B, and 24C. The dummy gates 124 may be removed by performing a first etching process and performing a second etching process after the first etching process.

In some embodiments, the first etching process is a dry etching process and the second etching process is a wet etching process. In some embodiments, the dry etching process includes using an etching gas such as CF₄, Ar, NF₃, Cl₂, He, HBr, O₂, N₂, CH₃F, CH₄, CH₂F₂, or a combination thereof. In some embodiments, the dry etching process is performed at a temperature in a range from about 20° C. to about 80° C. In some embodiments, the dry etching process is performed at a pressure in a range from about 1 mtorr to about 100 mtorr. In some embodiments, the dry etching process is performed at a power in a range from about 50 W to about 1500 W. The wet etching process may include using HF and NH₄OH. In some embodiments, wet etching process is performed at a temperature in a range from about 30° C. to about 200° C. In some embodiments, wet etching process is performed for a time in a range from about 20 seconds to about 400 seconds.

After the dummy gates 124 are removed, replacement gate stacks 150 a, 150 b are formed in the trenches 160. As shown in FIGS. 25A, 25B, and 25C, a high-k dielectric layer 162 a, 162 b for the N-type FinFET structure 102 and P-type FinFET structure 104 is deposited. In some embodiments, the high-k dielectric layer 162 a, 162 b is or includes metal oxides, metal nitrides, metal silicates, transition metal-oxides, transition metal-nitrides, transition metal-silicates, or oxynitrides of metals. Examples of the high-k dielectric material include, but are not limited to, hafnium oxide (HfO₂), hafnium silicon oxide (HfSiO), hafnium silicon oxynitride (HfSiON), hafnium tantalum oxide (HfTaO), hafnium titanium oxide (HfTiO), hafnium zirconium oxide (HfZrO), silicon nitride, silicon oxynitride, zirconium oxide, titanium oxide, aluminum oxide, hafnium dioxide-alumina (HfO₂—Al₂O₃) alloy, or other applicable dielectric materials.

In some embodiments, the high-k dielectric layer 162 a, 162 b may be formed from different materials for the N-type FinFET structure 102 and P-type FinFET structure 104. Patterned masks may be used to form the high-k dielectric layer 162 a, 162 b separately.

As shown in FIGS. 26A, 26B, and 26C, work function tuning layers 164 a, 164 b are formed over high-k dielectric layer 162 a, 162 b. The work function tuning layer 164 a, 164 b may be implemented to tune a work function. In some embodiments, the work function tuning layers 164 a, 164 b may be formed from different materials for the N-type FinFET structure 102 and P-type FinFET structure 104. Patterned masks may be used to form the work function tuning layers 164 a, 164 b separately.

The work function tuning layer 164 a may include N-type work function materials for the N-type FinFET structure 102. Examples of N-type work function materials include, but are not limited to, titanium aluminide (TiAl), titanium aluminum nitride (TiAlN), carbo-nitride tantalum (TaCN), hafnium (Hf), zirconium (Zr), titanium (Ti), tantalum (Ta), aluminum (Al), metal carbides (e.g., hafnium carbide (HfC), zirconium carbide (ZrC), titanium carbide (TiC), aluminum carbide (AlC)), aluminides, and/or other applicable materials.

The work function tuning layer 164 b may include P-type work function materials for the P-type FinFET structure 104. Examples of P-type work function materials include, but are not limited to, titanium nitride (TiN), tungsten nitride (WN), tungsten (W), ruthenium (Ru), palladium (Pd), platinum (Pt), cobalt (Co), nickel (Ni), conductive metal oxides, and/or other applicable materials.

In FIGS. 27A, 27B, and 27C, a metal gate electrode layer 166 is formed over work function tuning layer 164 a, 164 b. In some embodiments, metal gate electrode layer 166 is made of a conductive material, such as aluminum, copper, tungsten, titanium, tantalum, titanium nitride, tantalum nitride, nickel silicide, cobalt silicide, TaC, TaSiN, TaCN, TiAl, TiAlN, or other applicable materials. The metal gate electrode layer 166 may be formed by CVD, ALD, PVD, metal-organic chemical vapor deposition (MOCVD), plating, and/or other suitable processes.

In FIGS. 28A, 28B, and 28C, a planarization process, such as a CMP process, is performed after formation of the metal gate electrode layer 166 until the first spacer layer 128 and the second spacer layer 144 are exposed. As shown in FIG. 28B, the first spacer layer 128 covers sidewalls of the high-k dielectric layer 162 a, 162 b of the gate stacks 150 a, 150 b and a portion of top surface, sidewalls of the fins 110 a, 110 c, 110 b, 110 d at both ends of the channel region. The second spacer layer 144 covers the first spacer layer 128 at the sidewalls of the gate stacks 150 a, 150 b, top surfaces and sidewalls of the source/drain regions 134 a, 134 b, 134 c, 134 d, and top surfaces of the isolation regions 108.

Embodiments of the present disclosure provide a method of forming gate spacers by depositing a first spacer layer and a sacrificial layer prior to fin recessing, and depositing a second spacer layer after epitaxial growth. The methods may be used to form epitaxial source/drain regions for P-type FinFET structures or N-type FinFET structures. The method may prevent thickness loss of the gate spacers, may avoid sidewall loss in dummy gates, prevent corner damage in the gate structure, avoid mushroom defects, and prevent loss of the isolation regions.

One embodiment of the present disclosure provides method including forming a first dielectric layer over a fin structure and a dummy gate stack, the dummy gate stack being over the fin structure; conformally depositing a sacrificial layer over the first dielectric layer; performing an anisotropic etch process to expose portions of the fin structure while sidewalls of the dummy gate stack remain covered by the sacrificial layer and the first dielectric layer; growing source/drain regions from the exposed portions of the fin structure; removing the sacrificial layer to expose the first dielectric layer; and depositing a second dielectric layer on the first dielectric layer.

Another embodiment of the present disclosure provides a structure including a fin structure having source/drain regions on a substrate; a metal gate structure between the source/drain regions on the fin structure, wherein the metal gate structure includes a conformal high-k dielectric layer over the fin structure; and a gate electrode over the conformal high-k dielectric layer; a first gate spacer along a sidewall of the metal gate structure; and a second gate spacer along the first gate spacer and over the source/drain regions of the fin structure, wherein the first gate spacer is disposed between the metal gate structure and the second gate spacer.

Yet another embodiment of the present disclosure provides a method, including forming a dummy gate stack over a fin structure, forming a first spacer layer over the fin structure and the dummy gate stack, depositing a sacrificial layer over the first spacer layer, recessing the fin structure on both sides of the dummy gate stack, growing source/drain regions from the recessed fin structure, removing the sacrificial layer to expose the first spacer layer; and depositing a second spacer layer over the first spacer layer, the source/drain region, and the dummy gate stack; depositing a contact etch stop layer over the second spacer layer; removing the dummy gate stack to form a recess between remaining portions of the first spacer layer; and forming a metal gate stack in the recess.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method of forming a semiconductor device, the method comprising: forming a first dummy gate over a first fin structure and a second dummy gate over a second fin structure; forming a first spacer layer over the first dummy gate, the first fin structure, the second dummy gate, and the second fin structure; forming a first sacrificial layer over the first spacer layer; removing portions of the first sacrificial layer and the first spacer layer to expose the first fin structure; forming first source/drain regions on the first fin structure; removing the first sacrificial layer; forming a second sacrificial layer over the first spacer layer, the first dummy gate, the first source/drain regions, the second dummy gate, and the second fin structure; removing portions of the second sacrificial layer and the first spacer layer to expose the second fin structure; forming second source/drain regions on the second fin structure; and forming a second spacer layer over remaining portions of the first spacer layer.
 2. The method of claim 1, wherein, after removing portions of the second sacrificial layer and the first spacer layer to expose the second fin structure, portions of the first spacer layer remain along sidewalls of the second fin structure to form spacer portions.
 3. The method of claim 2, wherein forming the second source/drain regions comprises: recessing the second fin structure between the spacer portions; and epitaxially growing an epitaxial layer, the epitaxial layer protruding above the spacer portions.
 4. The method of claim 2, wherein sidewalls of the first fin structure in source/drain regions are free of the first spacer layer while forming the source/drain regions.
 5. The method of claim 1, a thickness of the first spacer layer is in a range from about 40% to about 60% of a combined thickness of the first spacer layer and the second spacer layer.
 6. The method of claim 1, wherein the first sacrificial layer comprises silicon nitride, silicon carbide nitride, silicon oxide, or silicon oxynitride.
 7. A method of forming a semiconductor device, the method comprising: forming a first fin structure in a first substrate region; forming a second fin structure in a second substrate region; forming a first dummy gate stack over the first fin structure; forming a second dummy gate stack over the second fin structure; forming a first gate spacer layer over the first fin structure, the first dummy gate stack, the second fin structure, and the second dummy gate stack; forming a first sacrificial layer over the first gate spacer layer in the first substrate region and the second substrate region; forming a first mask over the first sacrificial layer in the second substrate region; performing a first etch process to remove portions of the first sacrificial layer and the first gate spacer layer and to expose portions of the first fin structure, wherein after performing the first etch process remaining portions of the first gate spacer layer adjacent the first dummy gate stack form a first gate spacer, wherein after performing the first etch process portions of sidewalls of the first dummy gate stack remain covered by the first sacrificial layer and the first gate spacer; growing first source/drain region on the first fin structure; removing the first mask; removing remaining portions of the first sacrificial layer; forming a second sacrificial layer over the first gate spacer layer in the second substrate region and over the first gate spacer in the first substrate region; forming a second mask over the second sacrificial layer in the first substrate region; performing a second etch process to remove portions of the second sacrificial layer and the first gate spacer layer in the second substrate region, wherein after performing the second etch process remaining portions of the first gate spacer layer adjacent the second dummy gate stack form a second gate spacer, remaining portions of the first gate spacer layer adjacent the second fin structure form spacer portions on opposing sides of the second fin structure, wherein after performing the second etch process portions of sidewalls of the second dummy gate stack remain covered by the second sacrificial layer and the second gate spacer; growing second source/drain region on the second fin structure, wherein the second source/drain region is adjacent the second gate spacer; removing remaining portions of the second sacrificial layer; and forming a second gate spacer layer over the first gate spacer in the first substrate region and over the second gate spacer layer in the second substrate region.
 8. The method of claim 7, wherein the second source/drain region extends between the spacer portions.
 9. The method of claim 7 further comprising: prior to growing the first source/drain region, recessing the first fin structure; and prior to growing the second source/drain region, recessing the second fin structure.
 10. The method of claim 9, wherein recessing the second fin structure comprises recessing the second fin structure below an upper surface of the spacer portions.
 11. The method of claim 7, wherein the second gate spacer layer extends over the first source/drain region and the second source/drain region.
 12. The method of claim 11, wherein the second gate spacer layer directly contacts the spacer portions in the second substrate region.
 13. A semiconductor device comprising: a first transistor on a substrate, the first transistor comprising: a first epitaxial source/drain region over a first fin; a first metal gate structure adjacent the first epitaxial source/drain region, wherein the first metal gate structure includes: a first high-k dielectric layer over the first fin; and a first gate electrode over the first high-k dielectric layer; a first gate spacer along a sidewall of the first metal gate structure; and a second gate spacer along a sidewall of the first gate spacer and over the first epitaxial source/drain region, wherein the first gate spacer is disposed between the first metal gate structure and the second gate spacer; and a second transistor on the substrate, the second transistor comprising: a second epitaxial source/drain region over a second fin, the second epitaxial source/drain region having a small cross-sectional area than the first epitaxial source/drain region; a second metal gate structure adjacent the second epitaxial source/drain region, wherein the second metal gate structure includes: a second high-k dielectric layer over the second fin; and a second gate electrode over the second high-k dielectric layer; a third gate spacer along a sidewall of the second metal gate structure; a fourth gate spacer along a sidewall of the second gate spacer and over the second epitaxial source/drain region, wherein the third gate spacer is disposed between the second metal gate structure and the fourth gate spacer; and spacer portions along opposing sidewalls of the second epitaxial source/drain region.
 14. The semiconductor device of claim 13 further comprising an etch stop layer over the second gate spacer.
 15. The semiconductor device of claim 13, wherein the first gate spacer and the third gate spacer have a thickness in a range from 10 angstroms to 30 angstroms.
 16. The semiconductor device of claim 13, wherein the second gate spacer and the fourth gate spacer has a thickness in a range from 20 angstroms to 40 angstroms.
 17. The semiconductor device of claim 13, wherein the second gate spacer includes pores having a median radius in a range from about 0.4 nm to about 0.43 nm.
 18. The semiconductor device of claim 13, wherein the second gate spacer is a porous film having a porosity in a range from 2.00% to 3.50%.
 19. The semiconductor device of claim 13, wherein a thickness of the second gate spacer 40% to 70% of a total thickness of the first gate spacer and the second gate spacer.
 20. The semiconductor device of claim 13, wherein a height of the spacer portions is in a range from about 0 nm to about 10 nm. 